Reducing smoke in gas turbine engine exhaust



May 7, 1963 Filed April 13, 1960 A. H. LEFEBVRE ETAL 3,088,280

REDUCING SMOKE IN GAS TURBINE ENGINE EXHAUST 3 Sheets-Sheet l May 7, 1963 A. H. LEFEBVRE ETAL REDUCING SMOKE IN GAS TURBINE ENGINE EXHAUST Filed April 13 1960 5 Sheets-Sheet 2 NV M w 93$. dtkn Om SWN May 7, 1963 3,088,280

REDUCING SMOKE IN GAS I'URBINE ENGINE EXHAUST Filed April 15, 1960 A. H. LEFEBYRE ETAL 5 Sheets-Sheet 5 Filed Apr. 13, 1%9, Ser. No. 22,013 Claims priority, application Great Britain Apr. 17, 1959 '7 Ciaims. (Cl. 60-'39.65)

This invention comprises improvements in or relating to gas turbine engines and, more specifically, is concerned with combustion equipment of such engines.

Gas turbine engine combustion equipment may comprise an air casing of tubular or annular form and one or more flame tubes within the air casing. When the air casings of tubular form are used, there is usually a single flame tube per air casing, but, when the air casing is annular, there may be an annular flame tube or a series of flame tubes arranged in a ring within the air casing. In all forms of such combustion equipment, however, combustion occurs within the flame tube or flame tubes, air and fuel being delivered to one end, referred to herein as the inlet end, and combustion gases leaving at the opposite end, referred to herein as the outlet end; it is also usual to deliver part only of the air into the combustion space at the inlet end, the remainder of the air being introduced into the flame tube at points between the inlet and outlet ends.

In combustion equipment of such engines, combustion is initiated and largely effected in a primary zone adjacent an air inlet and is completed and the combustion gases cooled by addition of further air in a zone or zones downstream of the primary combustion zone.

It is known that a number of gas turbine engines produce an objectionably smoky exhaust. We have found that by injecting finely atomised coolant into the primary zone, in such a manner as to reduce the primary zone temperature by about 200, the smoke level in the exhaust can be markedly reduced. This eflect is due to evaporation of the finely atomised coolant in the primary zone and the resultant cooling of the combustion mixture. The rate of coolant injection necessary for smoke abatement is small and in any case should not be so great as to cause excessive cooling in the primary zone since this will lead to the flame being extinguished. Coolant injection in this way also leads to an improved life of the combustion equipment.

According to the invention, smoke abatement means for a gas turbine engine comprises means for injecting finely atomised Water uniformly into primary combustion zone of the flame tube or uniformly into the air entering the primary combustion zone at the upstream end of the flame tube in such a manner that suflicient of the water evaporates in the primary combustion zone to cool this zone by about 200 C.

Said means can comprise a fine atomiser producing a uniform distribution of Water droplets of the order of 50 to 60 microns diameter. Alternatively said means can comprise a simple spray producing a uniform distribution of droplets of the order of 200 to 300 microns and directed towards a discontinuous stationary surface element providing an entry into the primary zone, such as a swirl vane or a foraminous plate, so that the natural air blast atomisation occurring during operation of the engine will reduce at least some of the droplets to a size of the order of 50 to 60 microns.

Under some operating conditions, for instance when the ambient air temperature is high, there is a drop in the thrust produced by the engine, and in previous arrangements the thrust has been restored by injecting a coolant itecl States Patent into the flame-tubes in the region of the tertiary zone, thus enabling more fuel to be injected and burnt. It is found, however, that such injection of coolant increases the amount of smoke generated by the engine.

When this injection of coolant is required to increase thrust, in accordance with this invention, we continue to inject the requisite amount of water into the primary zone to cool the primary zone and the additional coolant liquid is injected in one of two ways. Either the additional coolant is injected into the tertiary zone as in previous arrangements or means are provided for injecting the additional coolant liquid in the primary zone together with the water which is being used to eliminate smoke. In the latter case care must be taken to ensure that the additional water droplets are so large that they travel through the primary zone without evaporating and thus do not cause an excessive lowering of the temperature in this zone.

This invention therefore also comprises combustion equipment of a gas turbine engine incorporating means to introduce a coolant liquid, for example water or water/ methanol, into the combustion space both at the primary air entry to the combustion space and simultaneously at a point between the primary air entry and the combustion gas outlet. In one arrangement, coolant liquid is sprayed into the air prior to its entry into the flame tube and further coolant liquid is sprayed into the flame tube adjacent the outlet end thereof.

Some embodiments of this invention will now be described With reference to the accompanying drawings in which:

FIGURE 1 is an axial section through gas turbine combustion equipment provided with coolant injection means,

FIGURE 2 is a view in the direction of arrow 2 on FIGURE 1 with parts broken away.

FIGURE 3 is a View similar to FIGURE 1 showing a second form of coolant injection means,

FIGURE 4 is a section through a form of injector for use in the arrangement of FIGURE 3,

FIGURE 5 is a graph,

FIGURE 6 is an axial section through a portion of a gas turbine combustion equipment showing a third form of coolant injection means, and

FIGURE 7 is a sectional view taken on the line 77 of FIGURE 6.

The forms of combustion equipment illustrated in FIGURES l and 2 and in FIGURE 3 are of the turbo-annular kind, that is of the kind comprising an annular air casing and a series of flame tubes arranged in a ring within the air casing.

The air casing comprises an outer annular Wall 10 which joins the downstream end of an outer wall 11, forming part of the diflfuser outlet of the compressor of the engine, to a turbine casing 12. The air casing also comprises an inner annular Wall 13 which is formed as an extension of the inner wall 14 of the diffuser outlet and carries at its downstream end a diaphragm 15 to which inner ends of turbine inlet guide vanes 16 are connected.

Each of the flame tubes 17 is supported within the annular space between the walls 10, 13 so as to leave passages 18 for the flow of air from the diifuser 11, 14 around the outside of the flame tube. Each flame tube 17 has at its inlet end a structure 19 forming an air inlet passage 20 for primary combustion air, and has at points along its length apertures 21, 22 through which air enters the flame tube from the passages 18. Each flame tube 17 has associated with it a form of fuel injector 23 and in the drawings, the injector 23 is of the spray type for delivering an atomised spray of liquid fuel into the primary combustion zone 24 to be burnt with 3 the primary air entering the flame tube through passage 20. The combustion products together with additional air entering the flame tube through apertures 21, 22 leaves the flame tube 17 at its outlet end through nozzle 25 to enter the turbine. Fuel is supplied to the injector 23 through pipe 26.

The present invention provides a coolant injection arrangement which enables a reduction of the smoke appearing in the engine exhaust and, if desired, under operating conditions when coolant injection is necessary or desired for thrust restoration, enables this to be achieved without production of excessive smoke in the engine exhaust. This is achieved in the arrangements shown by introducing a small quantity of the coolant liquid into the primary air so as to evaporate in and thereby to reduce the temperature in the primary combustion zone 24 to 'a value at which little or no smoke is produced, and, when thrust restoration is required, by also introducing a larger quantity of the coolant liquid into the flame tube downstream of the primary combustion zone 24. a

In the arrangement illustrated in FIGURES 1 and 2, the coolant liquid is injected to secure both smoke abate- 'ment and thrust restoration, and is water obtained from a manifold 39 encircling the diffuser 11, 14 and having first branches 31 leading from the manifold 30 to spray devices 32 (one per flame tube 17) which are disposed within the diffuser 11, 14 in line with and upstream of the primary air inlet passages 20 and which produce a finely atomised spray of coolant liquid into the air passing to the primary combustion zone, and having second branches 33 leading to spray devices 34 which are mounted on the air casing wall angularly between the flame tubes and which spray coolant liquid through the apertures 22 into the tertiary zones of the flame tubes 17 on each side of it. t

It is found that, in this way, the primary air does not contain so much coolant liquid as to cause excessive lowering of the temperature in the primary zone 24 and extinction of the flame, as might happen if the whole of the coolant liquid were injected into the primary air, and at the same time the mixture in the primary combustion zone 24 is cooled sufficiently to reduce substantially or to avoid smoke generation. At the same time by use of the coolant injecting arrangement, the total quantity of coolant injected can be such that good thrust restoration is obtained. The primary combustion zone temperature should not be reduced by substantially more than about The coolant injection means illustrated in FIGURE 3 is suitable for use either Where coolant injection is eifected for smoke abatement purposes only, or is for both smoke reduction and thrust restoration purposes.

In this arrangement, the coolant liquid is obtained from a manifold 130 having branches 131 leading to spray devices 132. When smoke reduction alone is required the central small orifice 133 is employed and this is fed by the central pipe 131 via passage 134, inclined passages 135, manifold 136 and short passages 137 to the passage 133, the water being swirled and atomised through the orifice 138, this water will be sufficiently finely atomised so that the whole of it is evaporated in the primary zone, reducing the primary zone temperature by about 200 C. and thus preventing any substantial smoke formation.

If thrust boost is required the outer manifold 139 supplies the outer passages 139 (FIGURE 4) and the water passes via manifold 140 and passages 141, 142, 143, to an annular swirl chamber 144, the water being atomised by the orifice 145. The atomisation will be less fine than occurs when using orifice 138 and the water droplets formed by the orifice 145 pass through the primary zone and are evaporated further downstream to cool the tertiary zone and to assist in providing thrust boost.

The same smoke reducing effect can be achieved by spraying water from a simple jet'(not an atomising orifree) on to a suitable discontinuous element such as the swirl vanes of the combustion chamber or a plate with a number of space holes in it put in place of the swirl vanes. Such an arrangement is shown in FIGURES 6 and 7 of the drawings in which parts similar to those illustrated in FIGURE 1 are indicated by the same reference characters. A conventional water or coolant sprayer 32a is disposed within the air inlet passage 2t) downstream of the air compressor and upstream of the fuel injector 23 and swirl vanes 19a so that the water or other coolant is entrained with the incoming air before it hits the swirl vanes. The portion of the spray which hits the plate or the swirl vanes is atomised by the air blast effect and is sufficiently finely atomised to achieve the desired cooling of the primary combustion zone.

FIGURE 5 is a graphical illustration of droplet size being plotted against volume. Trace 40 is the droplet size spectrum for a small orifice nozzle suitable for smoke abatement alone and it will be seen that the droplets have diameters below 50 microns. Trace 41 is the droplet size spectrum from a spray nozzle such as is shown in FIG- URE 4 and it will be seen that a small'proportion of the droplets have a diameter below 50 microns and that the greater proportion have a diameter greatly exceeding 50 microns.

When using water injection for thrust boosting the flame tube is subjected to a very high thermal loading and this has the effect of drastically shortening flame tube life. By injecting water at the upstream end and thus reducing the temperature in the primary combustion zone considerably, the thermal loading and the resultant stress on the flame tube is very much decreased particularly at the hottest part of the tube and this has the eflfect of considerably increasing flame tube life.

We claim:

1. In a gas turbine engine comprising an air compressor, combustion equipment including an air casing'hav- .flame tube to receive combustion products therefrom,

and an exhaust assembly connected to receive exhaust gases from the turbine; smoke abatement means for reducing smoke in the exhaust gases comprising swirling means disposed in the air inlet of the primary combustion zone, injecting means disposed downstream of the air compressor in the air inlet stream from the compressor and upstream of the fuel delivery means and the swirling means to deliver coolant liquid to the air in the air inlet means upstream of the swirling means so that the coolant liquid and the compressed air flow together through the swirling means so that the coolant liquid is directed onto the swirling means and the swirling means imparts to the coolant liquid and the compressed air a swirling motion to commingle thoroughly the coolant liquid and the compressed air with one another and with the fuel and products of combustion in the primary combustion zone so as to reduce substantially the temperature in the primary combustion zone as compared with the temperature when liquid injection is not effected, said swirling means comprising a discontinuous stationary surface element and said injecting means comprising a spray producing a uniform distribution of droplets which contact said element as they pass through the swirling means so that the natural air blast atomization occurring during operation of the engine will reduce at least some of the droplets as ,to size, said element distributing said droplets uniformly throughout the primary combustion zone.

2. In a gas turbine engine, smoke abatement means according to claim 1, wherein the discontinuous stationary surface element is a swirl vane at the direct air inlet to the flame tube.

3, In a gas turbine engine, smoke abatement means as claimed in claim 1, said injecting means comprising a liquid atomizer producing a uniform distribution of liquid droplets of the order of 50 to 60 microns diameter throughout the primary zone, said atomizer being disposed between the air inlet means of the air casing and the direct air inlet of the flame tube and delivering into air flowing through said direct air inlet.

4. In a gas turbine engine, smoke abatement means according to claim 1 comprising also means to inject further coolant liquid into the flame tube to evaporate downstream of the primary combustion zone.

5. In a gas turbine engine, smoke abatement means according to claim 4, the means injecting further coolant liquid injecting into air flowing through the primary combustion zone and producing large coolant liquid droplets which pass through the primary combustion zone without evaporating.

6. In a gas turbine engine, smoke abatement means according to claim 4, comprising a coolant liquid manifold having first branches which lead to first spray devices in line with and upstream of the direct air inlet of the flame tube, and having second branches leading to second spray devices spraying through apertures in the flame tube Walls.

7. In a gas turbine engine comprising an air compressor, combustion equipment including an annular air casing having air inlet means at one end connected to receive air compressed within the compressor and a ring of flame tubes each of which extends within the air casing and defines a combustion space, which combustion space at its end adjacent the air inlet means includes a primary combustion zone, each of said flame tubes having a direct air inlet from the air casing into the primary combustion zone and apertures downstream of the primary combustion zone, means to deliver fuel into the primary combustion zones to be burnt with the air flowing through the direct air inlet, a turbine connected to said flame tubes to receive combustion products therefrom, and an exhaust assembly connected to receive exhaust gases from the turbine; smoke abatement means for reducing smoke in the exhaust gases comprising swirling means in the form of discontinuous stationary surface elements disposed in the air inlet of the combustion zone of each flame tube, first injecting means disposed downstream of the air compressor in the air inlet stream from the compressor and upstream of the fuel delivery means and the swirling means to deliver coolant liquid to the air in the air inlet means upstream of the swirling means so that the coolant liquid and the compressed air flow together through the swirling means to direct the coolant liquid onto the swirling means to be atomized thereby and delivered in a finely atomized liquid form directly into the primary zone of each flame tube and the swirling means imparts to the atomized coolant liquid and the compressed air a swirling motion to commingle thoroughly the coolant liquid and the compressed air with one another and with the fuel and the products of combustion in the primary zone so as to distribute the coolant liquid uniformly throughout the primary zone to be evaporated therein to reduce substantially the temperature in the primary zones as compared with the temperature when liquid injection is not effected, said first injecting means comprising first spray devices in line with and upstream of the direct air inlets of the flame tubes, a coolant liquid manifold having first branches leading to said first spray devices, and second injecting means to inject further coolant liquid into said flame tubes to evaporate downstream of the primary combustion zones of the flame tubes comprising second spray devices disposed angularly between the flame tubes for spraying coolant liquid through said apertures into the flame tubes downstream of the primary combustion zones, said coolant liquid manifold having second branches leading to said second spray devices.

References Cited in the file of this patent UNITED STATES PATENTS 2,016,921 Goddard Oct. 8, 1935 2,168,313 Bichowsky Aug. 8, 1939 2,536,600 Goddard Jan. 2, 1951 2,598,544 Holman May 27, 1952 2,662,373 Sherry et al Dec. 15, 1953 2,712,221 Pouchot July 5, 1955 2,773,350 Barrett Dec. 11, 1956 2,847,825 Spears Aug. 19, 1958 2,916,877 Walter Dec. 15, 1959 FOREIGN PATENTS 476,195 Great Britain Dec. 3, 1937 704,669 Great Britain Feb. 24, 1954 

1. IN A GAS TURBINE COMPRISING AN AIR COMPRESSOR, COMBUSTION EQUIPMENT INCLUDING AN AIR CASING HAVING AIR INLET MEANS AT ONE END CONNECTED TO RECEIVE AIR COMPRESSED WITHIN THE COMPRESSOR AND A FLAME TUBE WHICH EXTENDS WITHIN THE AIR CASING AND DEFINES A COMBUSTION SPACE, WHICH COMBUSTION SPACE AT ITS END ADJACENT THE AIR INLET MEANS INCLUDES A PRIMARY COMBUSTION ZONE, SAID FLAME TUBE HAVING A DIRECT AIR INLET FROM THE AIR CASING INTO THE PRIMARY COMBUSTION ZONE, MEANS TO DELIVER FUEL INTO THE PRIMARY COMBUSTION ZONE DOWNSTREAM OF THE AIR INLET THERETO TO BE BURNED WITH THE AIR FLOWING THROUGH THE DIRECT AIR INLET, A TURBINE CONNECTED TO SAID FLAME TUBE TO RECEIVE COMBUSTION PRODUCTS THEREFROM, AND AN EXHAUST ASSEMBLY CONNECTED TO RECEIVE EXHAUST GASES FROM THE TURBINE; SMOKE ABATEMENT MEANS FOR REDUCING SMOKE IN THE EXHAUST GASES COMPRISING SWIRLING MEANS DISPOSED IN THE AIR INLET OF PRIMARY COMBUSTION ZONE, INJECTING MEANS DISPOSED DOWNSTREAM OF THE AIR COMPRESSOR IN THE AIR INLET STREAM FROM THE COMPRESSOR AND UPSTREAM OF THE FUEL DELIVERY MEANS AND THE SWIRLING MEANS TO DELIVER COOLANT LIQUID TO THE AIR IN THE AIR INLET MEANS UPSTREAM OF SWIRLING MEANS SO THAT THE COOLANT LIQUID AND THE COMPRESSED AIR FLOW TOGETHER THROUGH THE SWIRLING MEANS SO THAT THE COOLANT LIQUID IS DIRECTED ONTO THE SWIRLING MEANS AND THE SWIRLING MEANS IMPARTS TO THE COOLANT LIQUID AND THE COMPRESSED AIR A SWIRLING MOTION TO COMMINGLE THOROUGHLY THE COOLANT LIQUID AND THE COMPRESSED AIR WITH ONE ANOTHER AND WITH THE FUEL AND PRODUCTS OF COMBUSTION IN THE PRIMARY COMBUSTION ZONE SO AS TO REDUCE SUBSTANTIALLY THE TEMPERATURE IN THE PRIMARY COMBUSTION ZONE AS COMPARED WITH THE TEMPERATURE WHEN LIQUID INJECTION IS NOT EFFECTED, SAID SWIRLING MEANS COMPRISING A DISCONTINOUS STATIONARY SURFACE ELEMENT AND SAID INJECTING MEANS COMPRISING A SPRAY PRODUCING A UNIFORM DISRTRIBUTION OF DROPLETS WHICH CONTACT SAID ELEMENT AS THEY PASS THROUGH THE SWIRLING MEANS SO THAT THE NATURAL AIR BLAST ATOMIZATION OCCURRING DURING OPERATION OF THE ENGINE WILL REDUCE AT LEAST SOME OF THE DROPLETS AS TO SIZE, SAID ELEMENT DISTRIBUTING SAID DROPLETS UNIFORMLY THROUGHOUT THE PRIMARY CONBUSTION ZONE. 